Method for converting ethylene to alpha olefins in the presence of diphenylamine



Nov. 11, 1969 H. a. FERNALD ET AL METHOD FOR CONVERTING ETHYLENE TOALPHA OLEFINS IN THE PRESENCE 0F DIPHENYLAMINE Filed Nov. 9, 1966 UnitedStates Patent O 3,478,124 METHOD FOR CNVERTING ETHYLENE T ALPHA OLEFINSIN THE PRESENCE 0F DIPHENYLAMINE Herbert B. Fernald and Wiliiam Gall,Glenshaw, and

Harold E. Swift, Gibsonia, Pa., assignors to Gulf Research & DevelopmentCompany, Pittsburgh, Pa., a corporation of Delaware Filed Nov. 9, 1966,Ser. No. 593,156 int. Cl. C07c 3/10 U.S. Cl. 260683.15 5 Claims ABSTRACT0F THE DISCLOSURE A method for reducing solid polymer formation andincreasing catalyst efficiency in a process for the conversion ofethylene to liquid alpha olefins with an organometallic catalystcomprising performing said process in the presence of diphenylamine.

This invention relates to a method for reducing solid polymer formationin a process for the conversion of ethylene to liquid alpha olefins byperforming said process in the presence of diphenylamine or a derivativethereof.

In a process for the conversion of ethylene primarily to liquid normalalpha olefins having from about 4 to 30 or 40 carbon atoms in thepresence of an organometallic catalyst, such as triethylaluminum, asmall but highly deleterious quantity of solid polyethylene polymer isformed which deposits on reactor surfaces, interfering with heattransfer and necessitating frequent shutdowns of the reactor for removalof said polymer. In accordance with the present invention we have foundthat the presence of diphenylamine during the reaction inhibitsformation of said polymer without any substantial adverse effect uponthe efiiciency of the process. Any amount of diphenylamine whichinhibits polymer forma tion can be employed. For example, theconcentration of diphenylamine in the charge can be between about 0.25and 500 parts per million, generally, and between about 2 and 100 partsper million, preferably.

The step-wise conversion of gaseous ethylene to higher straight chainnormally liquid olefins having the double bond in the terminal or alphaposition, proceeds as follows:

etc. This polymerization occurs catalytically in the presence oforganometallic compounds, such as aluminum alkyls, which participate inthe reaction. As the reaction proceeds in the presence of excessethylene, an increasing quantity of gaseous ethylene is converted toliquid olefin so that the density of the reaction system progressivelyincreases. The chemistry of the alpha olefin process can be described interms of three major reactions. In the propagation (growth) reaction, analkyl group on an aluminum atom containing n ethylene units can add anethylene molecule to become an alkyl group of n|1 ethylene units, asfollows:

ice

The transalkylation (displacement) reaction which occurs concurrentlywith the growth reaction consists of two steps. These are, first,thermal decomposition of an aluminum alkyl group to a hydride plus alphaolefin followed by a rapid reaction of the hydride with ethylene toregenerate an ethyl group which can start another growth cycle. Thethermal decomposition is much slower than reaction of ethylene with ahydride and, therefore, iS the rate-determining step for the Over-allreaction.

Al--H The growth and displacement reactions occur repeatedly as long asthere is unreacted ethylene present. Therefore, the reaction isadvantageously afforded a very high residence time. As long as there isfree ethylene in the presence of catalyst in the reactor under reactionconditions, each mole of catalyst present will produce additional normalalpha olefin product. Therefore, a long residence time is conducive to ahigh alpha olefin yield per mole of catalyst, i.e., a high catalystefficiency.

The third reaction is similar to the first except that the aluminumalkyl adds a product alpha olefin, rather than ethylene, to form abranched chain aluminum alkyl group. However, this structure is veryunstable and rapidly decomposes to form a hydride and an olefin ofvinylidene structure.

The decomposition is so rapid compared to the addition of anotherethylene molecule to the branched alkyl that essentially all reactionsof this type result in an olefin of vinylidene structure andregeneration of an aluminum ethyl group. As a result, there will be few,if any, alpha olefins with branching beyond the beta carbon.

Low temperature favors of the growth. reaction and will result in ahigher average molecular weight product. At high tempeartures, theaverage molecular weight will be lower `because the transalkylationreaction predominates The proportion of C12 alpha olefin in the producttends to remain relatively constant with temperature changes within themost preferred range of this invention, with lower temperatures favoringa relatively higher proportion of product above C12 and highertemperatures favoring a relatively higher proportion of product belowC12.

It is believed that the higher molecular weight alpha olefins producedat temperatures below reaction temperatures may be precursors to thesolid polymers which it is the purpose of the present invention toinhibit. Therefore, in performing the process of the present inventioncold ethylene charge is preheated substantially to full reactiontemperature, i.e., to within about 5 F. to 10 F. of reactiontemperature, prior to addition of catalyst thereto and commencement ofthe reaction. For example, vvhen the reaction is performed continuouslyin a. tubular reactor surrounded by a heat exchange medium, coldethylene is charged to the inlet end of the tube and permitted to becomepreheated. The catalyst is injected into the tube at the downstreamposition therein at which ethylene has substantially reached fullreaction temperature. In this manner, production of relatively highmolecular weight alpha oleiins is avoided.

In view of the fact that the production of normal alpha olens is theobject of the above reactions, ethylene is the sole olen which can beemployed in the charge. The normal alpha oleiins produced will have fromfour to about 40 carbon atoms and will be primarily liquid withpractically the only solid polymer produced being an undesiredby-product which is inhibited in accordance with the method of thepresent invention. The normal alpha oleiins produced, particularly theC12, C14 and C16 alpha olelins, have high utility for the production ofdetergents.

The catalyst employed in the alpha olefin process can be delined by thefollowing structural formula: M',L Mb Rc Xd, wherein M is a metalselected from the alkali or alkaline earth metals and a can be either 0or one; M is a metal selected from the group consisting of aluminum,gallium, indium and beryllium and b can be either 0, one or two, exceptthat a+!) is at least one; R is selected from the group consisting of.monovalent saturated aliphatic or alicyclic radicals, monovalentaromatic radicals or any combination thereof; X is selected from thegroup consisting of hydrogen and halogen. The sum of c and d is equal tothe total valences represented by the metals, and X is a halogen c mustbe at least one. Examples of catalysts which can be employed includeetc. The `catalyst can be used as such, but preferably is employed withabout 70 to about 98 percent by weight thereof of an inert hydrocarbonsolvent such as saturated aliphatics (n-pentane, isopentane, hexane,n-heptane, isooctane, n-dodecane, merusol oil, paraflinic oils,kerosene, etc.), alicyclics such as cyclohexane, cyclopentane, etc.,aromatics such as benzene, toluene, etc. Since it is desired to producea liquid alphaolen product rather than a relatively high molecularweight solid polymer, the catalyst should be substantially free oflcatalyst components other than the catalysts defined above, such as,for example, TiCl4, which tend to cause production of relatively highmolecular yweight solid polymers. The amount of catalyst required hereinis not critical and can be from about 1x10-1 to about 1x10"2 moles permole of ethylene.

The temperature of the reaction can 4range from about 285 F. to about615 F., generally, from about 350 F. to about 430 F., preferably, andfrom about 380 F. to about 400 F., most preferably. The upper range ofpressure employed is not `critical and can be as high as about 1000atmospheres or even higher, but the lower pressure range, however, iscritical. The pressure should be suficiently high that most of thealpha-olelin product is a liquid under reaction conditions and so thatthe catalyst and most of the ethylene are dissolved or dispersed in saidliquid. As soon as liquid alpha-oleiin product is produced, the catalysttends to entirely dissolve therein. It is important to have as high aspossible a concentration of ethylene in the phase containing thecatalyst, otherwise liquid olefin product rather than ethylene will tendto react with the catalyst to produce vinylidenes. Therefore, thepressure should be sufficiently high to force as much ethylene aspossible into the liquid phase together with the catalyst. After therehas been a conversion of 55 to 60 percent of the ethylene, there issufficient liquid product to dissolve substantially all the ethylene andproduce a single homogeneous phase in the reactor. Thus, the pressure inthe reactor must at all times be at least about 500 to 1000, andpreferably at least about 2000 pounds per square inch gauge.

When it is desired to terminate the reaction, the product is withdrawnfrom the tubular reactor and is reduced in temperature and pressure,whereupon most of the gaseous olens are flashed off. The liquid productis then treated in any suitable manner to deactivate the catalyst andthe -desired product fractions are recovered. The catalyst may bedeactivated, for example, by contact .with suliicient acid, base, wateror alcohol to react stoichiometrically with the catalyst. When an acidor base is employed an aqueous layer is formed, which is then separatedfrom the organic layer, and the remainder, including solvent for thecatalyst, can be separated into its component parts by distillation. Ifdesired, the catalyst can be deactivated by contact with oxygen orhalogens or any other material which reacts with and suitably destroysthe catalytic activity of organometallic compounds. In a preferredmethod the aluminum catalyst is removed from the alpha-olefin product byreaction with caustic solution to form Na2OAl2O3 plus parain as follows:

It is shown in Ser. No. 153,815, iiled Nov. 2l, 1961, now abandoned,that the amount of the desired normal alpha olefin in the product isalways greater when the polymerization reaction is carried out in atubular or coil reactor rather than in a single continuous stirredautoclave or series of stirred autoclaves for a given total conversionof ethylene to some kind of polymer. That application explains that inorder to achieve high selectivity toward normal alpha olens thereactants and product should flow substantially as a column through thetube whereby there is a minimum of backmixing so that the percentage ofnormal alpha-olefin product increases throughout the length of thereactor. Since a given molecule of aluminum alkyl catalyst can undergogrowth and transalkylation reactions repeatedly, it is important thatethylene charge and catalyst be permitted a high residence time in orderto achieve a high catalyst efficiency, i.e., the production of a largeamount of normal alpha oleiins per mole of aluminum alkyl catalystcharged. A high residence time and avoidance of backmixing is mostconveniently achieved by utilizing a very long tubular reactor.

Example 1 A series of tests were conducted to determine the polymerinhibiting effect of diphenylamine and other materials in an alpha olenprocess. The effect of the production of even a small amount of polymerin an alpha olefin process is very great in terms of tube fouling,causing interference with heat transfer and requiring periodic reactorshutdowns in order to clean the tubes. These disadvantageous effectsoccur even though the amount of ethylene converted to polymer is anextremely small fraction of the amount of ethylene converted to thedesired alpha olefins. Therefore, if tests were to be performed underconventional operating conditions, the test period would have to beextensive in order for sufficient polymer to be produced in relation toalpha oleiin yield to render the measurements reliable. Furthermore,tests which extend over an unduly long period would consume relativelylarge amounts of ethylene and catalyst before a reliable measurementcould be obtained.

Therefore, a test procedure was devised to accelerate the production ofpolymer and provide an indication of the effectiveness of diphenylamineand other materials full reaction temperature of 392 F. The pressure wasthen brought to 500 pounds per square inch gauge by the addition ofethylene. As ethylene was converted either to polyethylene or to alphaolens fresh ethylene was added so that the pressure of 500 pounds persquare inch upon polymer inhibition. These tests employed the digaugewas maintained throughout the reaction period. phenylamine and othermaterials under polymer produc- The reaction was allowed to proceed for8 hours at which ing conditions much more severe than those ordinarilytime the prOdUCt WaS discharged through 1 llter fOr Colencountered in analpha olefin process in which the dileelorl 0f the Polylrlel- The amountof ethylene l'eaoted phenylamine of this invention is adapted to beutilized, 10 was determined by the ditference in the amount of ethyleneThe test procedure was devised on the theory that metered into theautoclave and the amount of ethylene polymerization in an alpha olefinreactor is encouraged discharged at the end of the test period. Theautoclave because of formation of a co-catalyst in the system by rewasdisassembled and all the polymer on inside autoclave action betweentriethylaluminum and metal oxides on Surfaces WaS Collected andProcessed With the Polymer oxidized reactor metal surfaces, such as, forexample, from the llter to reITloVe SolVeht and Product olels in oxidesof molybdenum, nickel, iron, chromium, copper, Order t0 determine theWelght Of dry Polyethylene Proaluminum, etc., followed by reaction ofethylene with said duced irl the eS- The Polyethylene Produced Was eX'co-catalyst to produce said polymer. These co-catalysts do Pressed 21SParts Per million based orl the total ethylene not tend to form withmetals in non-oxidized reactor reacted tubes, such as reactor tubeswhich have been freshly acid The effeCUVefleS of dlphehylalome 3S aPolymer 1h' washed. Based upon this theory, a number of metal oxidesh1b1-t0r Was de rmlfled by COfPPamg the results obtamed were testedtogether with triethylaluminum as catalysts by mcrporatmgdlphenl/lamllfle 1 /fh? cyclohexane S01' for Solid polyethyleneformation one of the best c0m vent with the results obtained in asimilar test except that binations tested for encouragement of polymerformation no polymer mhlblor Wasf presin m the cyclclhexnefol' was acommercial colloidal aluminum oxide and tri- 25 Vent' Test-s were a 5.0pr Orme O comparet e e ec ive' eth lalumium Therefore this combinationWa tilized ness of diphenylamine in the cycloheXane solvent against Il tt d .b d b l s u the use of a cyclohexane solvent to which had beenadded m1 e Is s escrl e e OW' various other compounds containing sulfurand/ or nitronf e test's 3'0 grams of the commercfal colloidal gen.Furthermore, tests were performed to show the alumfnum Oxld? Plusfboutlograms (6-0 Welght Percent) 30 effectiveness of a hydiogenatedsulfurand nitrogen- 0f methylalummum m a cyclohexane Solvent Vas Chargedcontaining lubricating oil derived from. a natural crude to a one-gallonautoclave equipped Wlth a Slrrfrl a hot' in a cyclohexane solvent as apolymer inhibitor. A full tom Outlet 1111, inlet 111165 fOr addlngethylene, a thermodescription of the lubricating oil is presented inExample well for a thermocouple to measure temperature, and an 2 of Ser.No. 593,214 led on Nov. 9, 19616. outlet for a Pressure gauge Someethylene WS Charged 35 The results of the tests performed in accordancewith to the autoclave and then the temperature was brought t0 the abovetest description are presented in Table 1, below.

TABLE i Catalyst Polymer efficiency, Produced, Grams p.p.m. EthyleneBased Converted on Total per Gram of Ethylene Triethyl Inhibitor AmountReaeted Aluminum Test' l Cycloliexane used as a catalyst solvent with no2, 000-2, 500 -120.

inhibitor present.

Materials which significantly reduce polymer production 2 Sulfur andnitrogen-containing hydrogenated 20ml 325 126.

lubricating oil derived from a natural einde.

3 do 40ml 49 133.

Phenothinzine 0.25 giri 231 89.

5 H 0.5 gin 282 109.

6 Bmercaptobenzothiazole 0.1 gm 91 109.

N Il C-SH 7 Diplienyl amine 0.2 gm 526 162.

TABLE `l-Continued Catalyst Polymer efficiency, Produced, Grams p.p,m.Ethylene Based Converted on Total per Gram of Ethylene TriethylInhibitor Amount Reacted Aluminum Test- S Dodecylsulde 10 gin 280 129.

CizHQaS-Cw-'zs Materials which reduce polymer production but which alsoseverely reduce catalyst efficiency 9 4,4'methylene bis 2,6 ditertiarybutyl phe11ol 0.1 gm 852 68,

l0 Phenothiazine (formula above) plus 4,4'meth 0.5 gm. euch. 1,200 20.

ylene bis 2,6 ditertifn'y butyl phenol.

l1 Quinoline 0.2 gm 2, 360 50.

12 Benzyl disulfide 0,2 giu 433 67.

13 Thiobeuzanilide 0.2 gm (373 91.

S H ll N C 14 Diethyl aniline. 0.2 gm 815 36.

15 Tliiobarbiturie acid 0.2 gm 1,020 41.

C is

5:0 I1N\ /NI- I C ll S Materials which deactivate the catalystcompletely 16 Thioacetaniido 0.2 gm No reaction.

S ClIa-C-NHn 17 Thianrhrene 0.2 gm Do.

18 Benzoquinone 0.2 gm D0.

O ll /C\ l) ll l(?\C C Il TABLE 1Continued Catalyst Polymer eicieney,Produced, Grams ppm. Ethylene Based Converted on Total per Gram ofEthylene Triethyl Inhibitor Amount Reacted Aluminum Test ....... 2,4,6,Trmethyl pyridine- 0.2 gm- DD.

CH3 CH3 20 Styrene 0,2 gm Do.

CH2=CH2 21 Thiourea 0.2 gm D0.

ll HgN-C-NHa 22 Diphenyl ether- 0.2 gm Do.

23 Dibutyl p-cresol 0.2 gm Do.

24 Thiopheno 0.2 gm Do.

HIC- H1B H CH S Table 1 shows that diphenylamine is highly effective ininhibiting polymer production while presenting no signitcantly adverseeffect upon catalyst efficiency in an alpha olefin process.

The accompanying drawing shows la single tubular re actor system whereinethylene is charged to a very long tubular reactor through a ow controlvalve 12. Tubular reactor 10 is disposed substantially entirely withinouter shell 14. Cooling Water is charged to shell 14 through line 16.Level control valve 18 maintains a constant water level within the shellwhich completely submerges reactor 10. A relatively small stream oftriethylaluminum catalyst, together with diphenylamine dissolved in asuitable solvent is pumped by positive displacement action to anintermediate point 22 in coil 10 through line 32 and valve 34 so thatthe region 24 of said coil upstream from point 22 serves as an ethylenepreheat zone and the region 26 of said coil downstream from point 22serves as a reaction zone. Point 22 is essentially the point in saidreactor coil closest to the inlet end wherein the ethylene issubstantially effectively preheated to the reaction temperature.Thereafter, regulation of steam pressure Within shell 14 by means ofsteam pressure control valve 28 in line 30 establishes the temperatureof the boiling water throughout shell 14 and maintains a uniform reactortemperature substantially throughout the length of reaction zone 26 ofthe coil 10. Reaction zone etlluent comprising predominantly normalalpha olefins, unreacted ethylene, and catalyst is discharged throughreactor pressure control valve 36, whereat the pressure is reduced tobetween about and 1,000 pounds per square inch gauge, and is thendischarged through cooling chamber 38 whereas product temperature isreduced to the lowest practical temperature While still maintaining theproduct in ia liquid state, i.e., to about 150 F., `'by means of Watercharged through line 40 and removed through line 42. Finally, productwhich is cooled and at a reduced pressure is passed through line 44 anda product measuring device 46, such as a flow recorder or chromatograph,and is then discharged through line 48 to a caustic treatment chamber,not shown, for removing the catalyst from the desired normal alphaolefin product by reacting the catalyst with caustic to produce sodiumaluminate and parains.

In order to achieve the highest conversion of ethylene to normal alphaolen per mole of catalyst used, the length of the reactor is made aslong as possible and is `only limited by practical and economic sizerestrictions of outer shell 14, and by pressure drop. For example, tube10 can comprise between about 500 and 10,000 feet of about onetofour-inch pipe. There are a number of reasons for utilizing a very longtubular reactor. First, a very long tubular reactor permits excellentheat transfer for removal of heat of reaction. Secondly, itadvantageously reduces backmixing for the reason explained above.Thirdly, a long reactor length permits achievement of `a high catalystefficiency because of additional conversion per mole of catalyst.Finally, a long reactor length tends to minimize the percentage ofparain in the alpha olefin product. The inal reason is based upon thefact that upon separation of the alkyl aluminum catalyst by treatmentwith caustic the alkyl components of the catalyst are converted toparaffns which have boiling points close to those of the most desiredalpha-olefin components yof the product and are therefore diicult toremove from the desired normal alpha olens. Since the absolute amount ofparains produced is fixed by the quantity of catalyst used, the greaterthe quantity of alpha olens produced `with said catalyst the smallerwill be the percentage of paratiins in the product.

The steam pressure in shell 14 is maintained at about between 50 and 500pounds per square inch, generally, and at about between and 340 poundsper square inch, preferably. The reactants in reaction zone 26 aregenerally at a temperature only about 3 F. to 15 F. above the bathtemperature. As noted above, the reaction temperature not only affectsthe degree of conversion of ethylene but, more importantly, it alsoestablishes the molecular `weight distribution of the alpha-olefinproduct. Since relatively low lreaction temperatures favor conversion torelatively high molecular weight product it is important to preheat theethylene to within about 1 F. to F., generally, and 3 F. to 6 F.,preferably, of the coolant bath temperature prior to catalyst addition.It is believed that the relatively high molecular weight alpha olelinsproduced at low reaction temperatures grow into polymers which can foulthe downstream region of the reactor tube and thereby increase thefrequency of periodic reactor down times due to fouling because ofpolymer formation. For this reason, it is important not to add catalystto the reactor tube until the ethylene has been preheated to as near aspossible to reaction temperature, and at least to within about 10 F. ofreaction temperature.

Finally, the reactor tube should not be so long that more than about 75weight percent, generally, or more than about 60 weight percent,preferably, of the ethylene is converted to product. The reason is thatat high conversion levels, there arises excessive competition betweenolen product and ethylene in the growth reaction, whereby conversion tovinylidene compounds becomes excess1ve.

The pressure in the tubular reactor should be suciently high that thealpha olefin product is mostly liquid phase under reaction conditionsand the ethylene and catalyst is presumably dissolve-d or dispersed insaid liquid. Therefore, the pressure in the reactor tube should be atleast about 500 or 1000 pounds per square inch gauge. The pressure dropthrough the tube is between about 5 and 300 pounds per square inch.

Any derivative of diphenylamine which is effective for inhibitingpolymer formation can be used in the process of this invention. Forexample, a diphenylamine derivative having an alkyl group containingbetween about one and eighteen carbon atoms at one or more positions inthe benzene rings can be employed. Other diphenylamine derivativesinclude compounds which contain hydrogen, aryl, alkaryl or arylalkylsubstituents at one or more of the carbon atoms of the benzene rings.Derivatives include dicyclohexyl amine and cyclohexyl-phenyl amine.

Various changes and modifications can be made without departing from thespirit of this invention or the scope thereof as defined in thefollowing claims.

We claim:

1. A process for converting ethylene to alpha olens CTI having betweenabout 4 and 40 carbon atoms comprising contacting ethylene andtriethylaluminum catalyst substantially without charging a catalystwhich tends to produce solid polymers at a temperature between about 285F. and 615 F. and a pressure of at least about 500 pounds per squareinch in the presence of diphenylamine.

2. The process of claim 1 wherein the ethylene is preheatedsubstantially to reaction temperature before contact with the catalyst.

3. The process of claim 1 wherein between about 0.25 and 500 parts permillion of diphenylamine are charged to the reactor.

4. A process for producing alpha olens containing primarily betweenabout 4 and 40 carbon atoms comprising charging ethylene to a tubularreactor immersed in a heat exchange medium and preheating said ethylenesubstantially to reaction temperature, charging triethylaluminumcatalyst to said preheated ethylene substantially without chargingcatalyst which tends to produce solid polymers, maintaining a reactiontemperature between about 285 F. and 615 F. and a pressure of at leastabout 500 pounds per square inch, charging diphenylamine to said reactorand withdrawing an alpha olefin-containing product from said reactor.

5. A process for producing alpha olefins containing between about 4 .and40 carbon atoms comprising charging ethylene to a tubular reactorimmersed in a bath of pressurized boiling water, said subular reactorcomprising metals oxidized to the metal oxide state, preheating theethylene substantially to reaction temperature in said tubular reactor,charging triethylaluminum substantially without charging catalyst whichtends to produce solid polymers to the preheated ethylene, maintaining areaction temperature between about 285 F, and 615 F. and a pressure ofat least about 500 pounds per square inch, charging between about 0.25and 500 parts per million of diphenylamine to said tubular reactor, andwithdrawing an efuent stream containing said alpha olens from saidtubular reactor.

References Cited UNITED STATES PATENTS 2,220,930 11/1940` Kraus260-683.15 X 2,699,457 1/1955 Ziegler et al. 260-683.15 3,078,262 2/1963Herman et al. 3,310,600 3/1967 Ziegler et al 260-683-15 3,318,860 5/1967Eichenbaum 260-937 PAUL M. COUGHLAN, IR., Primary Examiner

